1. Field of the Invention
The present invention relates to the field of electrical devices, such as electrical components and/or housings for electrical components or electrical assemblies, which have a lead frame bonded to a main body of the electrical device. More particularly, the present invention is directed to such devices wherein the lead frame has a plurality of individual flat electrical leads which extend from insulating well structure of the main body and are intended for connection to other devices/structures.
This invention also relates to thermally stable connection arrangements and particularly, though not exclusively, to such connection arrangements for use in automotive environments.
2. Description of the Prior Art
Some prior electrical components and housings utilize lead frames bonded to insulating wall structure of a main body of the components/housings wherein the lead frame comprises a plurality of individual leads formed from flat sheet stock. An example of such prior structure is the conventional integrated circuit dual in-line package (DIP) in which two separate rows of individual leads extend from opposite insulating sidewalls of a main plastic molded body of the integrated circuit. Typically these leads extend outward and then downward with respect to the integrated circuit main body. End portions of these leads are subsequently bonded to other structures such as a conventional printed circuit board or ceramic circuit board. The leads of DIP lead frame typically comprise a series of parallel planar fingers of the lead frame which initially extend outward from the integrated circuit main body. Planar intermediate portions of the leads extend downward with respect to the main body and terminate in end portions of the leads to be bonded to a circuit board. Similar configurations have been utilized for protective housings for electrical components/assemblies. In such housings, insulating sidewall structures of the housing have inwardly extending leads which have intermediate portions extending downward so as to make connection, via end lead portions, to a circuit board positioned within the sidewalls.
Generally, the planar downwardly extending portion of the above noted individual leads, because it has a relatively thin thickness dimension, is able to absorb some thermal expansion stresses which may be generated between the component/housing and the other structure to which the leads are bonded. However, it has been noted that thermal cycling may cause lead bond failures at the end lead portions, especially for such leads located adjacent to the corners of the main body when the main body has a generally rectangular configuration.
In a known connection arrangement for use in an automotive environment a printed circuit on a substrate is mounted on a heat sink. The printed circuit substrate and heat sink are fixed in a housing. The housing incorporates a lead frame whose leads extend from the exterior to the interior of the housing where they are soldered to the printed circuit. Typically the housing, the printed circuit substrate and the heat sink all have different coefficients of thermal expansion. Thus a soldered connection between the lead frame and the printed circuit is subjected to mechanical stress caused by differential movements between the parts as the temperature changes In the relatively harsh physical conditions of an automotive environment such stresses over the course of hundreds of cycles between temperatures as extreme as -50.degree. C. and +150.degree. C. can often lead to joint failure due to shearing of a soldered joint.
It is known to make the leads longer and thinner in order for them to be more compliant and relieve some of the stress by absorbing some of the differential movement, but such changes often run counter to the requirements of minimizing the size of the arrangement or increasing its ruggedness.